Merge pull request #43297 from nextcloud/fix/db/dirty-read-cool-off

fix(db): Let dirty writes cool off

lib/private/DB/Connection.php

@@ -55,7 +55,9 @@ use OCP\Diagnostics\IEventLogger;
 use OCP\IRequestId;
 use OCP\PreConditionNotMetException;
 use OCP\Profiler\IProfiler;
+use Psr\Clock\ClockInterface;
 use Psr\Log\LoggerInterface;
+use function in_array;
 
 class Connection extends PrimaryReadReplicaConnection {
 	/** @var string */
@@ -67,6 +69,8 @@ class Connection extends PrimaryReadReplicaConnection {
 	/** @var SystemConfig */
 	private $systemConfig;
 
+	private ClockInterface $clock;
+
 	private LoggerInterface $logger;
 
 	protected $lockedTable = null;
@@ -83,6 +87,7 @@ class Connection extends PrimaryReadReplicaConnection {
 
 	protected ?float $transactionActiveSince = null;
 
+	/** @var array<string, int> */
 	protected $tableDirtyWrites = [];
 
 	/**
@@ -110,6 +115,7 @@ class Connection extends PrimaryReadReplicaConnection {
 		$this->tablePrefix = $params['tablePrefix'];
 
 		$this->systemConfig = \OC::$server->getSystemConfig();
+		$this->clock = \OCP\Server::get(ClockInterface::class);
 		$this->logger = \OC::$server->get(LoggerInterface::class);
 
 		/** @var \OCP\Profiler\IProfiler */
@@ -265,10 +271,19 @@ class Connection extends PrimaryReadReplicaConnection {
 	 */
 	public function executeQuery(string $sql, array $params = [], $types = [], QueryCacheProfile $qcp = null): Result {
 		$tables = $this->getQueriedTables($sql);
+		$now = $this->clock->now()->getTimestamp();
+		$dirtyTableWrites = [];
+		foreach ($tables as $table) {
+			$lastAccess = $this->tableDirtyWrites[$table] ?? 0;
+			// Only very recent writes are considered dirty
+			if ($lastAccess >= ($now - 3)) {
+				$dirtyTableWrites[] = $table;
+			}
+		}
 		if ($this->isTransactionActive()) {
 			// Transacted queries go to the primary. The consistency of the primary guarantees that we can not run
 			// into a dirty read.
-		} elseif (count(array_intersect($this->tableDirtyWrites, $tables)) === 0) {
+		} elseif (count($dirtyTableWrites) === 0) {
 			// No tables read that could have been written already in the same request and no transaction active
 			// so we can switch back to the replica for reading as long as no writes happen that switch back to the primary
 			// We cannot log here as this would log too early in the server boot process
@@ -280,7 +295,7 @@ class Connection extends PrimaryReadReplicaConnection {
 				(int) ($this->systemConfig->getValue('loglevel_dirty_database_queries', null) ?? 0),
 				'dirty table reads: ' . $sql,
 				[
-					'tables' => $this->tableDirtyWrites,
+					'tables' => array_keys($this->tableDirtyWrites),
 					'reads' => $tables,
 					'exception' => new \Exception('dirty table reads: ' . $sql),
 				],
@@ -335,7 +350,9 @@ class Connection extends PrimaryReadReplicaConnection {
 	 */
 	public function executeStatement($sql, array $params = [], array $types = []): int {
 		$tables = $this->getQueriedTables($sql);
-		$this->tableDirtyWrites = array_unique(array_merge($this->tableDirtyWrites, $tables));
+		foreach ($tables as $table) {
+			$this->tableDirtyWrites[$table] = $this->clock->now()->getTimestamp();
+		}
 		$sql = $this->replaceTablePrefix($sql);
 		$sql = $this->adapter->fixupStatement($sql);
 		$this->queriesExecuted++;